1. Field of the Invention
The invention relates to measuring solid particle number concentrations from engine or vehicle exhausts in real-time.
2. Background Art
Engine exhaust particles mainly consist of solid and volatile particles. Many studies show particles from diesel engine exhausts cause many health problems. To understand how particles impact human health, characteristics of particles from engines and vehicles should be investigated. Thus, the accurate measurement of particles emitted by modern diesel and gasoline vehicles is needed.
European PMP (Particle measurement programme) has recommended an approach to measure solid particle number emission from light-duty diesel vehicles. The system is shown in FIG. 1, and consists of a pre-classifier 10, a hot diluter (PND1) 12, an evaporation tube 14, a cold diluter (PND2) 16, and a condensation particle counter (CPC) 18. The pre-classifier 10 is used to keep the cutoff size of particles in 2.5 to 10 μm. By running the hot diluter 12 at a high dilution air temperature, and the evaporation tube 14 heating the sample in the range of 300 to 400° C., particles formed by volatile material and sulfate are vaporized to gas phase. By following with cold dilution with the cold diluter 16, all particles formed by volatile material and sulfate are removed. As a result, solid particles only move into the CPC 18 with the flow. The concentration of the solid particles is measured in the CPC 18.
Many factors, such as dilution ratios on the hot diluter (PND1) 12 and cold diluter (PND2) 16, solid particle penetration over the instrument, removal efficiency for volatile particles, etc., strongly influence the accuracy of the instrument. To have good accuracy on the measurement, accurate dilution ratios on the hot diluter (PND1) 12 and the cold diluter (PND2) 16, high penetration for solid particles, and high removal efficiency for volatile particles, should be achieved on the measuring system.
The condensation particle counter (CPC) has been widely used to measure particle number concentration. It has fast response time and is a real-time sensor. However, the experimental setup and operation procedure and calibration to use the CPC for measuring combustion engine or vehicle exhaust aerosols are pretty complicated. The accuracy of the measured results is strongly influenced by human factors, such as, the knowledge of the operator of combustion engines and aerosol science, etc. To make the CPC more reliable for engine or vehicle exhaust aerosol measurement, it is very important to simplify the experimental setup and operation procedure.
Background information may be found in U.S. Pub. No. 2006/0179960. This publication describes the concept of a wide range continuous diluter. Further background information may be found in “Real-time measuring system for engine exhaust solid particle number emission—Performance and Vehicle tests,” SAE Technical Paper No. 2006-01-0865, and in “Real-time measuring system for engine exhaust solid particle number emission—Design and Performance,” SAE Technical Paper No. 2006-01-0864.